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1. Field of the Invention
The present invention relates to hydraulic hammer reduction systems for vehicles such as railroad tank cars and the like. More particularly, the present invention relates to an improved hydraulic hammer reduction system that includes a plastic element disposed in an outlet tube at the upper end of the vehicle, said element being comprised of a series of spaced apart curved baffles affixed to opposite sides of an elongated body.
2. General Background of the Invention
Moving vehicles carrying a liquid load in a tank, such as for example railroad tank cars, when carrying liquids, must cope with problems associated with hydraulic hammer action, a phenomenon which occurs when a liquid in a confined area is subjected to an abrupt increase or decrease in speed.
Vehicles such as railroad tank cars are typically equipped with a safety vent nozzle and a device called a rupture disk. The rupture disk which is affixed to the top of the safety vent nozzle is used to seal the tank car under normal conditions. In events [such as fires] that can cause an increase of the internal pressure of a tank car, the rupture disk is designed to burst allowing the internal pressure to vent to the ambient. Once burst the excess pressure is relieved, protecting the tank car from a catastrophic failure, and complete loss of the product inside to the ambient.
The hydraulic hammer action created by the abrupt change in speed, mentioned earlier, is sufficient to travel up the safety vent nozzle and break the rupture disk. This allows a non-accident release of the product contained in the tank car. This release will cause unnecessary damage to the environment, the tank car, and injury to a person standing close to the tank car.
The rationale in utilizing such a system was that it was better to incur the relatively minor expense and danger associated with disk replacement and a minor spill than to have incurred the extensive expense and danger of tank car fracture and/or a major spill. However, as indicated, this has been far from a satisfactory solution and situation.
The hydraulic hammer reduction systems shown in U.S. Pat. Nos. 4,840,192 and 4,938,247 do function well; however, the baffles shown in those patents must be made of metal, as they are too weak if they are made of plastic. A safety vent for a railroad car which contains a surge protection is disclosed in U.S. Pat. No. 5,785,078. The following U.S. Patents are incorporated herein by reference: U.S. Pat. No. 4,840,192; 4,938,247; 5,785,078; and all referenced cited in those patents.
The apparatus of the present invention solves the problems confronted in the art in a simple and straightforward manner. What is provided is a hydraulic hammer reduction system, similar to that shown in U.S. Pat. Nos. 4,840,192 and 4,938,247, but an improved design with baffles shaped such that they can be made of plastic, yet still be strong enough to absorb mechanical energy without breaking. Preferably the baffles are made of plastic.
The present invention provides a vehicle for transporting a liquid commodity that includes a closed tank having an inside surface, an outside surface, a top, a bottom and an interior for containing a liquid commodity. A safety vent is mounted on the top of the tank on the outside surface and having a safety relief valve for allowing pressure to escape from the tank in the event of a pressure build up greater than the tank is rated for and before the tank can fracture.
The present invention provides a mechanical energy dissipation system for dissipating hydraulic hammer action in the safety vent. The apparatus includes a mechanical device of relatively small size in comparison to the size of the tank, the device being located in the line of flow between the valve and the liquid load in the tank. The device presents a series of diverging, impact surfaces to the liquid flow from the tank to the rupture disk, for dissipating the hydraulic hammer action of the liquid as it flows through the device.
The diverging impact surfaces are made of a non-metallic plastic material such that they are strong enough to absorb mechanical energy without breaking.
The mechanical device occupies less than and extends into less than about 1% of the interior volume of the tank.
The mechanical device preferably includes a one-piece plastic body having a core, and said diverging impact surfaces comprising a series of spaced apart baffles placed in succession and affixed to opposite sides of the core and integral therewith. The body projects into the tank car and out of the tank car leading to the valve assembly.
The baffles are preferably a series of spaced apart plates.
Each of the plates is preferably defined by a pair of surfaces that form an angle with each other that is preferably an acute angle.
The baffles preferably have a pair of surfaces that form an angle of between 0 and 60xc2x0 degrees with each other.
The present invention also provides a method of dissipating the hydraulic hammer action in a safety vent of a moving tank carrying a liquid load, such as for example, a railroad car, having a rupture disk assembly or safety relief valve.
The method includes providing a relatively small, mechanical energy dissipation device having a series of diverging, impact surfaces for dissipating hydraulic hammer action in the moving tank car. As part of the method, the mechanical device is attached in line between the liquid and the tank and the rupture disk of the rupture disk assembly causing any liquid to have passed through the mechanical device before it can reach the rupture disk.
In the method of the present invention, the device occupies less than and extends into less than about 1% of the interior volume of the tank.
With the method of the present invention, the kinetic energy of the moving liquid is dissipated as it passes through the mechanical device impacting against the diverging surfaces of the mechanical device and thereby dissipating the hydraulic hammer action.
With the method of the present invention, the diverging, impact surfaces are of a non-metallic, plastic material.
With the method of the present invention, the impact surfaces are strong enough to absorb mechanical energy without breaking.